1. Field of the Invention
The present invention relates to a tilt correcting apparatus for and a tilt correcting method of detecting the amount of disc tilt (hereinafter merely referred to as the “amount of tilt”) in an optical disc, such as a writable DVD+R and a writable DVD+RW, and making a tilt correction on the basis of the detected amount of tilt, and an information recording apparatus and an information recording/reproducing apparatus, such as a DVD recorder, including such a tilt correcting apparatus.
2. Description of the Related Art
On an information reproducing apparatus, such as a DVD player, it is extremely important to irradiate an optical disc which is set, such as a DVD, with laser light for reading, from a direction perpendicular to the recording surface of the optical disc, in order to optically read information, accurately. This is because the inclination, i.e., “tilt” of the information recording surface of the optical disc, such as a DVD, to the laser light deteriorates a reproduction signal, depending on the amount of tilt (i.e., a tilt amount or a tilt angle) as being the extent of the inclination, or the angle of tilt. Thus, conventionally, on a read-only optical disc, such as a DVD-ROM, the amount of tilt of the information recording surface is detected by using the amplitude of a Radio Frequency (RF) signal, which is detected in accordance with the presence of record information (i.e. recording pits). Then, at the time of actual reproduction of the record information, the irradiation angle of the laser light is fine-tuned so as to cancel the amount of tilt (which is referred to as a “tilt correction” herein as occasion demands) with respect to the information recording surface; namely, the laser irradiation angle to the information recording surface is set so as to increase the amplitude of the RF signal, to thereby prevent the deterioration of the reproduction signal by tilt.
On the other hand, even an information recording apparatus or an information recording/reproducing apparatus, such as a DVD recorder, at the time of recording, it is extremely important to irradiate an optical disc with laser light for writing, from a direction perpendicular to the information recording surface of the optical disc, in order to optically write information. This is because the presence of tilt causes a large light spot to be formed on the information recording surface, depending on the amount of tilt, to thereby deteriorate a writing signal. In this case, if the writable disc, such as a DVD+RW, is unrecorded, it is impossible to detect the RF signal corresponding to the record information, as in the above-mentioned DVD-ROM or the like. Thus, in place of the RF signal, the amplitude of a tracking error signal which uses land/groove tracks is used for the detection of the amount of tilt. For example, in reproducing the information on an optical disc in a wobble•land pre-pit manner, the signal amplitude of a RF difference signal (i.e. the tracking error signal) and the amplitude of a land pre-pit signal can be used, to thereby detect the amount of tilt (e.g. refer to Japanese Patent Application Laid Open NO. 2002-288859).
However, the irradiation angle of the laser light which gives a peak to the RF signal is not generally equal to the irradiation angle of the laser light which gives a peak to the tracking error signal. Namely, there is such a technical problem that the highly accurate tilt correction is essentially difficult or impossible from the detection of the amount of tilt by using the tracking error signal. Moreover, in order to detect the amount of tilt by using the tracking error signal, it is necessary to open tracking servo, for the detection of the amount of tilt at one point for recording, then, measure the tracking error signal, then, close the tracking servo, and then, perform a next detection. For such detection, it takes, e.g., several tenths of a second. Thus, if it is desired to obtain the distribution of the amount of tilt on the whole disc, it takes several seconds since the same detection is performed at a plurality of points for recording. Namely, there is also such a technical problem that the quick detection of the amount of tilt is essentially difficult.